Question

已知等差數(shù)列{an}的公差d≠0,且a1,a3,a9成等比數(shù)列,則=(　　)

(A)(B)(C)(D)

 

Answer 1

C

【解析】等差數(shù)列{an}中,a1=a1,a3=a1+2d,a9=a1+8d,因?yàn)?/span>a1,a3,a9恰好構(gòu)成某等比數(shù)列,所以有=a1a9,即(a1+2d)2=a1(a1+8d),解得d=a1,所以該等差數(shù)列的通項(xiàng)為an=nd.則的值為.